Ultrafast photoconductive detectors based on semi-insulating GaAs and InP

Photoconductive dipole antennas fabricated on semi-insulating (SI) GaAs and SI-InP were used to detect terahertz (THz) pulses. The responses of these long-carrier-lifetime photoconductive detectors were compared to that of the photoconductive antenna fabricated on a low-temperature grown GaAs (LT-GaAs) with a subpicosecond carrier lifetime. The SI-InP-based photoconductive detector showed a higher responsivity and a better signal-to-noise ratio (SNR) than the LT-GaAs-based photoconductive detector at low gating laser powers. The SI-GaAs-based detector, however, showed a responsivity comparable to that of the LT-GaAs photoconductive detector only at very weak gating laser power, and the SNR of the SI-GaAs-based detector was poor for overall gating laser powers due to the high background noise originating from a large amount of stray photocurrent.